This invention relates to new terpolymers which can be used, for example, as additives improving the cold-flow properties of lubricating oils and various hydrocarbon oils.
It also relates to lubricating oil compositions comprising these terpolymers.
It also relates to hydrocarbon oils such as diesel oils, domestic fuel oils, heavy fuel oils (fuel oils No. 2), residual fuel oils or crude oils whose congealing point or freezing point is decreased by adding terpolymers soluble in these hydrocarbon oils.
The lubricating oil compositions adapted to internal combustion engines and to automatic power transmissions require, in the base oil, associated additives exhibiting a number of properties, in addition to their lubricating power. These properties comprise decreasing the freezing point or the congealing point of the oil, heat stability and resistance to oxidation, rust and corrosion inhibition, dispersion of the carbon deposits and of the insoluble materials formed by fuel combustion and oil oxidation, neutralization of the acid materials formed by oil oxidation and finally improvement of the viscosity index.
Various compositions have been described in the literature, which comprise copolymers obtained by the addition reaction of alpha-olefins with dicarboxylic alkenes, which are thereafter esterified with long chain saturated straight-chain alcohols, so as to make the copolymers soluble in hydrocarbon oils in appropriate manner; polyamino compounds are then added, so as to form dispersion agents or agents improving the viscosity index of lubricants.
Polymeric acrylic esters are also known to decrease the freezing point or the congealing point of lubricating oils, and a known factor having a particularly great influence in that case is the length of the lateral alkyl chains; the presence of a sufficient number of long lateral alkyl chains is apparently decisive to obtain sufficient solubility of the additive in hydrocarbon oils.
Finally, it is also known that, although copolymers of acrylic esters with certain alpha-olefins, such as ethylene or propylene, can be obtained easily, it is impossible to obtain copolymers of acrylic esters having a high diisobutylene content, taking the too low reactivity of this monomer into account.
It has now been found that copolymers of acrylic esters containing an important proportion of diisobutylene can be obtained easily (particularly in moderate conditions of temperature and pressure) by adding an ethylenically unsaturated dicarboxylic compound, in at least equimolar proportion with respect to diisobutylene, to the monomer mixture.
It has also been found that the resultant terpolymers greatly improve the cold-flow properties of lubricating oils, the presence of diisobutylene units in these additives improving their solubility in hydrocarbon oils.
Another advantage of the terpolymer additives of the invention, as compared with the anti-freeze additives of the prior art, containing acrylic esters, lies in the possibility to also improve the dispersion effect, the presence of carboxylic anhydride or carboxylic acid units in the terpolymers of the invention allowing a further reaction with (poly-)amino and/or (poly-)hydroxy compounds.
Finally the use of these terpolymers as additives having both improved properties for decreasing the freezing point or the congealing point and dispersion properties for lubricants is advantageous from the economic point of view, since, on the one hand, incorporating important amounts of diisobutylene and maleic anhydride into acrylic esters contributes to decreasing the final price of the additive, without disadvantage as concerns the properties, and, on the other hand, the dispersant properties of the anti-freeze additive provide for a reduction or suppression of an additional use of conventional dispersant additives for lubricating oils.
It is well known that certain hydrocarbon oils contain such compounds as paraffins, asphaltenes or resins which make them viscous and impart unacceptable flow properties. These oils behave at low temperature as non-newtonian fluids; they have a congealing or freezing point, as well as particular hysteresis properties which greatly limit their use, for example, as fuel oils, and their production, particularly, as far as crude oil are concerned.
A prior technique which obviates these disadvantages consists of subjecting the hydrocarbon oils to dewaxing or deasphalting processes; however these processes are often very expensive.
Another technique which is used to decrease the viscosity or the freezing point of the hydrocarbon oils having a high content of asphaltic and/or paraffinic compounds consists of diluting them by adding lighter hydrocarbon oils or distillates. This is also an expensive technique since light oils have a far higher cost than heavy oils.
A third technique, which is very often the least expensive and has the highest efficiency, consists of adding small amounts of polymeric additives to fluidify the hydrocarbon oil or improve its cold-flow properties.
Among the numerous additives proposed in the prior art, mention may be made of polymers or copolymers based on .alpha.-olefins or diolefins, optionally hydrogenated and/or alkylated, the polymers or copolymers of unsaturated esters, such as acrylates or methacrylates, as well as certain copolymers of .alpha.-olefins with unsaturated esters, such as copolymers of ethylene or propylene with vinyl acetate or with acrylates and methacrylates. These additives are known to decrease the limit filterability temperature of diesel oils or domestic fuel oils, and to improve the cold-flow properties of certain highly paraffinic fuel oils or crude oils. However these additives are not very efficient to improve the fluidity and the flow properties of heavy hydrocarbon oils, such as high-boiling fuel oils, fuel oils No. 2, residues of atmospheric distillation (residual fuel oils) or highly asphaltenic crude oils.
It has now been found that the cold-flow properties of these hydrocarbon oil compositions (particularly fluidity, in the case of heavy oils) can be improved by adding small amounts of certain terpolymers, as hereinafter defined.